Process for producing a multi-layer printer wiring board

ABSTRACT

The present invention is directed to an inter-laminar adhesive composition containing a liquid epoxy resin, a polyfunctional epoxy resin having a softening point higher than a lamination temperature of the adhesive and with two or more epoxy groups within the molecule; and a latent epoxy curing agent initiating a reaction at a temperature higher than the lamination temperature. The adhesive composition optionally contains a liquid resin other than the liquid epoxy resin and/or an organic solvent and the liquid resin includes the liquid epoxy resin, the organic solvent or both constituting from 10 to 55% by weight of the composition.  
     This inter-laminar adhesive composition allows for the preparation of a multi-layer printed wiring board. The process for preparing the multi-layer printed wiring board is provided. The resulting multi-layer printed wiring board of the invention possesses excellent embedding properties in the internal-layer circuit, excellent surface smoothness and can be provided at high productivity levels in a building up process using the present adhesive.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a divisional of U.S. application Ser. No. 09/721,664filed Nov. 27, 2000; which is a continuation of U.S. application Ser.No. 08/999,332, filed Dec. 29, 1997, now abandoned.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an inter-laminar film adhesivefor multi-layer printed wiring boards, capable of integrally carryingout the coating process of an inner-layer circuit pattern and thefilling process of a resin in a superficial via hole and/or athrough-hole simultaneously on a multi-layer printed wiring board of abuild-up type where a conductive layer and an insulation layer arealternatively built up; and a process for producing a multilayer printedwiring board using the same.

[0004] 2. Discussion of the Background

[0005] Conventional processes for producing a multi-layer printed wiringboard generally comprise lamination pressing through several prepregsheets produced by impregnating an insulation adhesive layer glass clothimpregnated with an epoxy resin to prepare the cloth at B stage andobtaining inter-laminar communication by way of through-holes. However,the process is costly and conducts heating and molding under pressurethrough lamination pressing, thus requiring large equipment and a longprocessing time. Additionally the process requires the use of glasscloth with a relatively high dielectric constant as the prepreg sheet,which limits the ability to reduce the inter-laminar thickness. Theprocess is also problematic because of the insulation concern due toCAF.

[0006] As one way to overcome such problems, attention has recently beenfocused on buildup production technique of multi-layer printed wiringboards, comprising alternately laminating an organic insulation layer onthe conductor layer of an internal-layer circuit board. Japanese PatentLaid-open No. 7-202426 and 8-157566 disclose a method for producing amulti-layer printed wiring board, comprising coating and preliminarilydrying an underlining adhesive on an internal-layer circuit board with acircuit formed therein and bonding a copper foil or a copper foil withan adhesive on the board.

[0007] Additionally, in Japanese Patent Laid-open No. 8-64960, a methodis disclosed for producing a multi-layer printed wiring board,comprising coating and preliminary drying of an underlining adhesive andattachment of a film additive adhesive followed by curing under heating,scrubbing with an alkaline oxidant, and plating to form a conductorlayer. Because the underlining adhesive layer is formed in an ink formby these methods, however, the possibility of dust contamination intothe adhesive layer during the processes is high, which causes circuitfailure due to disconnection and short circuiting.

[0008] As a method with no use of an underlining adhesive, JapanesePatent Laid-open No. 7-202418 discloses a method for producing amulti-layer printed wiring board, by forming an adhesive layer,comprising a high molecular epoxy resin and an epoxy resin, as liquidson a copper foil, and attaching the resulting copper foil with theadhesive onto an internal-layer circuit board. This method isproblematic, however, in that the copper foil with the adhesive isreadily wrinkled or damaged during lamination. Additionally, any of theabove-noted methods has two major drawbacks from the respect ofworkability and characteristic properties of the final product, in that(1) these methods require a hole filling process, by means of a holefilling resin and the like, if through-holes are present on aninternal-layer circuit board and (2) voids readily develop insuperficial via holes if they are present.

SUMMARY OF THE INVENTION

[0009] Accordingly, one object of the present invention is to provide aninter-laminar adhesive film that is useful in multi-layer printed wiringboards, among other things, and gives excellent embedding properties inthe internal-layer circuit.

[0010] A further object of the present invention is to provide aninter-laminar adhesive film that provides excellent surface smoothnesswhen used in production of multi-layer printed wiring boards.

[0011] A further object of the present invention is to provide a processfor production of a multi-layer printed wiring board at highproductivity levels using the inter-laminar adhesive film in a build-upprocess.

[0012] These and other objects of the present invention have beensatisfied by the discovery of an inter-laminar adhesive film formulti-layer printed wiring boards, the adhesive film being capable ofintegrally carrying out the coating of the internal-layer circuitpattern and the filling of a resin in the superficial via holes and/orthrough-holes for a build-up process of producing a multi-layer printedwiring board, and a process of producing a multi-layer printed wiringboard by using the adhesive film at a high productivity level.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Various other objects, features and attendant advantages of thepresent invention will be more fully appreciated as the same becomesbetter understood from the following detailed description whenconsidered in connection with the accompanying drawings in which likereference characters designate like or corresponding parts throughoutthe several views and wherein:

[0014]FIG. 1 depicts an appearance of the adhesive film for multi-layerprinted wiring boards of the present invention, which is formed on asupport base film (1) and is embedded in an internal-layer circuit board(4) with a circuit pattern and a through-hole (5).

[0015]FIG. 2 depicts an appearance of the adhesive film for multi-layerprinted wiring boards after the process of FIG. 1, at an embedded statein an internal-layer circuit board (4) from which is peeled off asupport base film (1), at a prestage to form a copper foil or aconductor layer through plating.

[0016]FIG. 3 depicts an appearance such that the scrubbable resincomposition (6) and the inter-laminar adhesive film for multi-layerprinted wiring boards, formed on the support base film (1), are at astate of being embedded in the internal-layer circuit board (4) with acircuit pattern and a through-hole (5).

[0017]FIG. 4 depicts an appearance of the adhesive film for multi-layerprinted wiring boards after the process of FIG. 1, at an embedded statein an internal-layer circuit board (4) from which is peeled off asupport base film (1), at a prestage to form a copper foil or aconductor layer through plating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention relates to an inter-laminar adhesive filmfor multi-layer printed wiring boards, comprising a support film baselaminated on an internal-layer circuit board having a pattern processedthereon, and a resin composition that is solid at ambient temperature(hereafter referred to as a “solid resin composition”), which islaminated on the surface, wherein the solid resin composition containsat least 10% by weight of a resin with a lower softening point than thelaminate temperature and is of a thickness larger than the thickness ofthe electric conductor in the internal-layer circuit and resin flow ofthe solid resin composition at the laminate temperature satisfies on ofthe following: (1) it is at least of the thickness of the electricconductor of the internal-layer circuit, (2) it is of the depth of asuperficial via hole if present in the internal-layer circuit, or (3) itis ½-fold or more the depth of a through-hole if present in theinternal-layer circuit singly or in combination with a superficial viahole. Within the context of the present invention, when a resin isreferred to as a solid resin, it indicates that the resin is solid atambient temperatures. Conversely, if a resin is referred to as a liquidresin, it indicates that the resin is in a flowable or liquid state atambient temperatures.

[0019] The present invention also provides a process of producing themulti-layer printed wiring board using the inter-laminar adhesive filmand a process of producing the same.

[0020] When the inter-laminar adhesive film for multi-layer printedwiring boards of the present invention comprises an epoxy resincomposition, the present inter-laminar adhesive film meets one of thefollowing compositions:

[0021] (1) the solid resin composition comprises the following essentialcomponents;

[0022] (A) an epoxy resin that is liquid at ambient temperature (aliquid resin);

[0023] (B) a polyfunctional epoxy resin having a softening point higherthan the laminate temperature and with two or more epoxy groups withinthe molecule; and

[0024] (C) a latent epoxy curing agent initiating a reaction at atemperature higher than the laminate temperature; and wherein the resincomposition may or may not contain a liquid resin other than thecomponent (A) and/or an organic solvent and wherein the liquid resinincluding the component (A) and/or the organic solvent in totalconstitute from 10 to 55% by weight of the total adhesive; or

[0025] (2) the solid resin composition comprises the following essentialcomponents;

[0026] (A) a liquid epoxy resin;

[0027] (B′) a polyfunctional epoxy resin having a softening point lowerthan the laminate temperature and with two or more epoxy groups withinthe molecule;

[0028] (C) a latent epoxy curing agent initiating a reaction at atemperature higher than the laminate temperature; and (D) a binderpolymer with a weight average molecular weight within a range of 5,000to 100,000; and

[0029] wherein the resin composition may or may not contain a liquidresin other than the component (A) and/or an organic solvent;

[0030] wherein the liquid resin including the component (A) and/or theorganic solvent in total constitute from 10 to 55% by weight of thetotal adhesive; and

[0031] wherein the component (D) is 5 to 50% by weight of the totaladhesive.

[0032] The solid resin composition used in the present inter-laminaradhesive composition includes a resin composition comprising athermosetting resin and/or a polymer as the principal component, whereinthe resin composition is softened under heating and has the ability toform a film. The solid resin composition also is capable of satisfyingthe characteristic properties required for inter-laminar insulationmaterials, such as heat resistance and electric properties, after thecomposition is thermally set. For example, the composition includes, butis not limited to epoxy resins, acrylic resins, polyimide resins,polyamide imide resins, polycyanate resins, polyester resins, andthermosetting polyphenylene ether resins. The composition can containthese resins individually or in combinations of two or more thereof andcan also be prepared as an adhesive film layer of a multi-layerstructure. Among epoxy resins with a higher reliability and good costperformance as an inter-laminar insulating material, preference is givento the epoxy resin composition of the present invention as describedbelow. Additionally, the thermosetting process can be omitted if athermoplastic engineering plastic such as thermoplastic polyimide isused.

[0033] The solid resin composition necessarily contains at least 10% byweight of a resin with a softening point lower than the temperatureduring lamination. Below 10% by weight, it is difficult to embed theresin into a through-hole and/or a superficial via hole in theinternal-layer circuit without occurrence of a void. Preferably, theliquid resin and/or the solid resin with a softening point lower thanthe laminate temperature are within a range of 10 to 90% by weight, intotal.

[0034] The solid resin composition may or may not contain an inorganiccomponent at a preferable content of 30% by weight or less. Through theaddition of such inorganic compounds, an inter-laminar adhesive film formulti-layer printed wiring boards having excellent laser piercingproperties can be produced.

[0035] In addition to the principal components in the resin composition,use may be made of other conventional additives. For example, use may bemade of inorganic fillers such as barium sulfate, calcium carbonate,barium titanate, silicon oxide powder, amorphous silica, talc, clay, andmica powder; flame-retardant agents such as antimony trioxide andantimony pentoxide; organic-fillers such as silicon powder, nylonpowder, nylon powder, and fluorine powder; thickening agents such asasbestos, orben, and benton; defoaming agents and/or leveling agents,such as silicon compounds, fluorine compounds, and polymers andadhesiveness providing agents such as imidazoles, thiazoles, triazoles,and silane coupling agents. If necessary, a desired use may be made ofconventional coloring agents such as dyes and pigments, including, butnot limited to, phthalocyanine blue, phthalocyanine green, iodine green,disazo yellow, titanium oxide, and carbon black. The resulting adhesivefilm can provide an excellent laser piercing property, by limiting theinorganic components to 30% by weight or less in the resin composition.If the inorganic components are about 30% by weight, vias with smalldiameters of 100 μm or less have poor shapes after the use of a CO₂laser or a UV laser, with resultant poor plating adhesion thus creatinga problem in connection reliability. Additionally, the laser processingrate is disadvantageously lowered from the respect of productivity.

[0036] As to the solid resin composition in the inter-laminar adhesivefilm for multi-layer printed wiring boards of the present invention, amost preferred embodiment comprising an epoxy resin will now bedescribed. The liquid epoxy resin as the component (A) in accordancewith the present invention is an essential component to impartflexibility to the resulting adhesive film and impart thermalflowability during lamination onto an internal-layer circuit board. Morespecifically, preference is given to a bisphenol A epoxy resin with anepoxy equivalent of about 200, a bisphenol F-type epoxy resin with thesame level of epoxy equivalent, a phenol novolak-type epoxy resin withthe same level of epoxy equivalent, or an epoxy-modified fluid rubber orrubber dispersed fluid epoxy resin. Additionally, reactive diluents suchas allylglycidyl ether, glycidyl methacrylate, alkylphenyl glycidylether and polyhydric alcohol-type glycidyl ether and other conventionalepoxy resins, such as alicyclic epoxy resins, may be used singly or incombinations of two or more thereof. Together with the other liquidresin components described below and the residual organic solvents,these liquid epoxy resins are required to be within a range of from 10to 55% by weight in the resin composition. Below 10% by weight, theflexibility and cut processability of the resulting adhesive film are sopoor that the film is barely handleable. Above 55% by weight, thefluidity of the adhesive film at ambient temperature is so high thatproblematic oozing occurs due to edge fusion or the support film and theprotective film start to peel. A liquid resin component with a lowviscosity should be used in a lower amount, while such resin componentwith a high viscosity should be used in a comparatively higher amount.However, the range of adding a scrubbing component corresponding to thecomponent (E) is limited. Furthermore, the residual organic solvent iswithin a range of 0.3 to 10% by weight.

[0037] The “polyfunctional epoxy resin with two or more epoxy groupswithin the molecule” as the components (B) and (B′) in accordance withthe present invention is required to provide various properties such asheat resistance, chemical resistance, and/or electric propertiessatisfactory for an inter-laminar insulation material. The resin for useas components B and B′ can be any conventional polyfunctional epoxyresin meeting the above requirements. Suitable polyfunctional epoxyresins include bisphenol A epoxy resins, bisphenol F epoxy resins,bisphenol S epoxy resins, phenol novolak epoxy resins, alkylphenolnovolak epoxy resins, bisphenol epoxy resins, naphthalene epoxy resins,dicyclopentadiene epoxy resins, an epoxylated product of a condensate ofphenols with an aromatic aldehyde having a phenolic hydroxyl group,triglycidyl isocyanurate, and alicyclic epoxy resins. Furthermore, usecan be made of the epoxy resins after bromination, in order to impartflame retardancy. These polyfunctional epoxy resins require a componentwith a softening point higher than the temperature during lamination,whereby the thermal fluidity during attachment can be suppressed and thesurface smoothness after heating and curing becomes excellent. Because aliquid polyfunctional epoxy resin is contained as component (B′), therange of the addition thereof is limited in the same manner as forcomponent (A). The component is a polyfunctional epoxy resin with two ormore epoxy groups within the molecule and with a softening point nothigher than the laminate temperature. In order to produce aninter-laminar adhesive film for multi-layer printed wiring boards usingthe component (B′), the essential components thereof should be (D) abinder polymer with an average molecular weight within 5,000 to 100,000,in addition to (A) a liquid epoxy resin and (C) a latent epoxy curingagent initiating a reaction at a temperature higher than the laminatetemperature. The resin composition may or may not contain a liquid resinother than the component (A) and/or an organic solvent, wherein theliquid resin including the component (A) and/or the organic solvent intotal constitute from 10 to 55% by weight of the adhesive and thecomponent (D) in the resin composition is from 5 to 50% by weight of thecomposition.

[0038] The component C “latent epoxy curing agent” in accordance withthe present invention includes amine curing agents, guanidine curingagents, imidazole curing agents or epoxy adducts thereof ormicrocapsulated products thereof. An epoxy curing agent shouldpreferably be selected having a longer pot life below ambienttemperature to initiate a reaction at a temperature higher than thetemperature during lamination during the elevation of the temperature,such that sufficient thermal fluidity during lamination can bemaintained to readily determine the conditions for lamination. Thereaction initiation temperature is defined as an exothermic peakinitiation temperature measured by differential calorimetry (DSC) at atemperature elevation rate of 5° C./min, provided that 5 parts by weightof a curing agent is added to 100 parts by weight of bisphenol Adiglycidyl ether (epoxy equivalent: 186-192) followed by homogenousdissolution or dispersion. The reaction initiation temperature forvarious exemplary compounds is as follows; dicyandiamide (initiationtemperature; 165-175° C.), 2-phenyl-4-methyl-5-hydroxymethyl imidazole(initiation temperature; 135-145° C.),2-phenyl-4,5-bis(hydroxymethyl)imidazole (initiation temperature;145-155° C.), 2,4-diamino-6-(2-methyl-1-imidazoylethyl)-1,3,5-triazine(initiation temperature; 110-120° C.),2,4-diamino-6-(2-methyl-1-imidazolylethyl)-1,3,5-triazine•isocyanuricacid adduct (initiation temperature; 125-135° C.), and2,4-diamino-6-(2-undecyl-1-imidazolylethyl)-1,3,5-triazine (initiationtemperature; 115-125° C.). The amounts of these latent epoxy curingagents to be added are within a range of 2 to 12% by weight of the epoxyresin. Below 2% by weight, curing is insufficient. Above 12% by weight,curing occurs too strongly so that the film gets too fragile. If theconditions for the latency and the reaction initiation temperature areprovided, a phenolic curing agent and a curing promoting agent may alsobe used, including, for example, phenol novolak resins, alkylphenolnovolak resins and curing promoting agents such as imidazole compoundsand organic phosphine compounds, more preferably including tetraphenylphosphoniumtetraphenyl borate and the like. The amount thereof to beadded is adjusted as follows; phenolic hydroxyl groups should be within0.6 to 1.0 equivalent per epoxy group in the epoxy resin; the curingpromoting agent should be at 0.5 to 2% by weight of the total of the tworesins. Furthermore, the individual latent epoxy curing agents describedabove may be used singly or in combinations of two or more thereof or incombination with conventional curing promoting agents.

[0039] In order to improve the mechanical strength and flexibility ofthe adhesive film for better handling, the component (D), namely the“binder polymer with a weight average molecular weight within a range of5,000 to 100,000” is required. If the weight average molecular weight isbelow 5,000, the effect on improving the mechanical strength andflexibility cannot be exerted; above 100,000, the solubility of thebinder in an organic solvent and the miscibility of the binder with anepoxy resin are deteriorated, so that the resulting film cannot be used.Preferably, the amount of component D to be added is within a range of 5to 50% by weight. Below 5% by weight, the mechanical strength andflexibility are not improved. Above 50% by weight, the thermal fluidityof the resulting film is deteriorated. Because the thermal fluidity ofthe resulting film can be suppressed when the film contains component D,the polyfunctional epoxy resin with a softening point higher than thelaminate temperature is not essential. Additionally, the binder polymerhelps prevent crossing over the support film. More 'specifically, thebinder polymer includes, but is not limited to phenoxy resins, which canbe optionally brominated, polyacrylic resins, polyamide resins,polyamide imide resins, polycyanate resins, polyester resins, andthermosetting polyphenylene ether resins. These can be used singly or incombinations of two or more thereof.

[0040] In order to efficiently perform wet scrubbing with an oxidant, onthe film surface after the adhesive film is cured under heating, atleast one scrubbing component selected from oxidant-soluble rubbercomponents, amino resins, inorganic fillers and organic fillers isnecessary. Examples of suitable rubber components include polybutadienerubber, modified polybutadiene rubber such as epoxy modified, urethanemodified, and (meth)acrylonitrile modified polybutadienes, and furtherincludes (meth) acrylonitrile butadiene rubber containing carboxylgroups and epoxy resins of acrylic rubber-dispersed type. Suitable aminoresins include melamine resins, guanamine resins, urea resins and alkyletherified resins thereof. Suitable inorganic fillers include calciumcarbonate, magnesium carbonate and magnesium oxide. Suitable organicfillers include powdery epoxy resins and cross-linked acrylic polymers,and additionally includes the aforementioned amino resins after thermalcuring and fine grinding. These scrubbing components are preferably usedwithin a range of 5 to 40% by weight in the resin composition. Below 5%by weight, the scrubbing potency is insufficient, while above 40% byweight, the electric properties, chemical resistance and thermalresistance of the resulting film are so poor that the film cannot bepractically used as an inter-laminar insulation material. Also, theadditive resin composition includes a component (F) which is a catalyzerfor non-electro-plating with metal, and is used as an additiveinter-laminar adhesive film having good properties for wet plating. Theexamples of the catalyzer include a metal powder such as palladium,gold, platinum, silver, copper, cobalt, tin and/or its halide, oxide,hydroxide, sulfide, peroxide, amine salt, sulfate, nitrate, salt oforganic acid, and chelates thereof. An inorganic material coordinatedwith one or more other metal(s) and/or its compound are preferably usedas catalyzer. The examples of the inorganic materials include powder ofalumina or carbon and so on. A diameter of the powder is within a rangeof from 0.1 to 50 μm. The catalyzer is preferably within a range of 0.05to 3% by weight in the resin composition.

[0041] An inter-laminar adhesive film having a two-layer structure formulti-layer printed wiring boards, with no such upper limit of thescrubbing component, is produced by laminating together a solidscrubbable resin composition essentially comprising the followingcomponents;

[0042] (A) a polyfunctional epoxy resin with two or more epoxy groupswithin the molecule;

[0043] (B) an epoxy curing agent; and

[0044] (C) at least one scrubbing component selected from the groupconsisting of a rubber component, amino resins, inorganic fillers andorganic fillers, and the resin composition described above in accordancewith the present invention, whereby the surface scrubbing potency withan oxidant and the reliability as an inter-laminar insulation materialcan be imparted in a simple fashion to the resulting adhesive film. Thethickness of the scrubbable resin composition is preferably less thanhalf of the total film thickness, more preferably within a range of 1 to15 μm, with respect to the flexibility and fine patterning of theresulting film and the reliability of the inter-laminar insulation. Asthe polyfunctional epoxy resin to be used as component (A), use is madeof those described above, with no preference for liquid or solid. As theepoxy curing agent, use is made of conventional curing agents such asamines, guanidines, imidazoles and acid anhydrides or epoxy adductsthereof. As the scrubbing agent, use is made of the same compounds ascomponent (E) at 5% by weight or more. And the catalyzer fornon-electro-plating with metal (F) is added to the resin composition at0.05% by weight or more.

[0045] The inter-laminar adhesive film in accordance with the presentinvention can be prepared by coating a resin-varnish dissolved in anorganic solvent using a base film as a support, drying the solvent byheating and/or hot air spraying to prepare a solid resin composition.The support base film includes polyolefins, such as polyethylene andpolyvinyl chloride; polyesters, such as polyethylene terephthalate;polycarbonates; as well as release papers and metal foils such as copperfoil and aluminum foil. The thickness of the support base film ispreferably 10 to 150 μm. The support base film is further processed witha release process (other than a mud process and a corona process). Asthe organic solvent, use may be made of ketones such as acetone, methylethyl ketone, and cyclohexane; acetate esters such as ethyl acetate,butyl acetate, Cellosolve acetate, propylene glycol monomethyl etheracetate, and Carbitol acetate; Cellosolves such as Cellosolve and butylCellosolve; Carbitols such as Carbitol and butyl Carbitol; aromatichydrocarbons such as toluene and xylene; and additionallydimethylformamide, dimethylacetoamide, and N-methyl pyrrolidone, singlyor in combination of two or more thereof. The amount of the residueorganic solvent is defined as weight decrement ratio, prior to and afterdrying in a dryer kept at 20° C. for 30 minutes.

[0046] The thickness of the solid resin composition is above thethickness of the conductor on the internal-layer circuit board to belaminated, and varies depending on the residual copper ratio in theinternal-layer circuit pattern, the board thickness, the through-holediameter, the superficial via hole diameter, the number of holes and thepreset value of the thickness of the insulation layer. Preferably, thethickness is within a range of the conductor thickness plus 10 to 120μm. If the board thickness is large and the resin filled volume of thethrough-hole is large, a thicker resin composition is necessary. Thethus formed adhesive film of the present invention, comprising the solidresin composition and the support base film is stored, as it is or isstored after a protective film is further laminated on the other face ofthe resin composition and is then rolled in. Suitable protective filmsinclude the same as for the support base film, for example, polyolefinssuch as polyethylene, polyvinyl chloride, and polypropylene; polyesterssuch as polyethylene terephthalate; and release papers. The thickness ofthe protective film is preferably 10 to 100 μm. Furthermore, theprotective film may satisfactorily be processed at a release process inaddition to the mud process and emboss process. As described below, theresin in the resin composition oozes during lamination, so that aportion of the support base film should be arranged at a width of about5 mm or more on both ends or a single end of the roll to prevent resinadhesion onto the laminate part and to permit peeling of the supportbase film to be readily done.

[0047] With reference to the drawings, a multi-layer printed wiringboard using the inter-laminar adhesive film of the present invention anda process for fabricating the board will now be described. For attachingthe adhesive film of the present invention onto a pattern processedinternal-layer circuit board, the protective film, if present, isremoved, and then, the solid resin composition (2) is laminated underpressure and heating (FIG. 1). By laminating under conditions such thatthe resin flow during lamination is above the thickness of the conductor(3) of the internal-layer circuit and above half of the through-hole (5)depth and/or the superficial via hole depth of the internal-layercircuit, the coating of the internal-layer circuit pattern and the resinfilling in the superficial via hole can be done simultaneously andintegrally. As the internal-layer circuit board (4), use is made ofglass epoxy and metal boards, polyester boards, polyimide boards,thermosetting polyphenylene ether boards and the like. The circuitsurface may preliminarily be subjected to a scrubbing process, ifdesired. Under reduced pressure, the lamination is performed bybatch-wise process or continuously by means of a roll. Preferably, boththe surfaces are laminated.

[0048] As described above, the lamination conditions can vary, dependingon the thermal melt viscosity and thickness of the solid resincomposition of the present invention, the through-hole diameter anddepth of the internal-layer circuit board, and/or the superficial viahole diameter and depth. Generally, the temperature for contact boardingis 70 to 200° C.; and the pressure therefor is 1 to 10 kgf/cm².Lamination is preferably done under reduced pressure of 20 mmHg or less.If the through-hole diameter is large and deep or if the board is of alarger thickness, the resulting resin composition is so thick thatlamination conditions at a high temperature and/or a high pressure arerequired. Generally, a board thickness up to about 1.4 mm and athrough-hole diameter up to about 1 mm are appropriate for good resinfilling. The surface smoothness of the resin composition afterlamination is better when the support base film (1) is thicker, whichis, however, disadvantageous for embedding the resin in-between thecircuit pattern with no voids. Preferably, therefore, the support basefilm (1) has a thickness the same as the conductor (3) thickness plus orminus 20 μm. When the surface smoothness and thickness of the resin onthe pattern are not sufficient because the conductor thickness on theinternal-layer circuit is thick or when a recess develops in the holebecause the diameters of the through-hole and the superficial via holeare too large, the inter-laminar adhesive film should be furtherlaminated thereon. After lamination, the film is cooled to aroundambient temperature to peel off the support base film.

[0049] After laminating the inter-laminar adhesive film for multi-layerprinted wiring boards (FIG. 2), the resin composition (2) is thermallycured if necessary, and then, a copper foil with an adhesive thereon ora copper foil is further laminated as an upper layer thereof underheating, thereafter integrating them all to prepare a multi-layerprinted wiring board. The curing conditions under heating can vary,depending on the types of materials of the internal layer circuit boardand the curing temperature of the copper foil having an adhesive thereonif used. The curing conditions are preferably selected within the rangesof 120 to 200° C. and 20 to 90 minutes.

[0050] In a further embodiment of the adhesive film according to thepresent invention, the adhesive film is laminated on an internal-layercircuit board (4) with a pattern processed, in the same manner asdescribed above, so that the resin composition containing the scrubbingcomponent (6) or catalyzer might be on the outer side (FIGS. 3 and 4).Thereafter, if necessary, the film is cured under heating, and a giventhrough-hole and/or via hole part is pierced by laser or drilling, andthe surface of the resin composition is scrubbed using a wet and/or dryprocess, if necessary. Then, the conductor layer is formed by dryplating and/or wet plating, to prepare a multi-layer printed wiringboard. The thermal curing conditions are preferably selected withinranges of 120 to 200° C. and 10 to 90 minutes. The dry scrubbing processof the surface of the resin composition includes mechanical polishingwith a polishing means such as an abrasive pad, sandblasting, plasmaetching and the like. Alternatively, the wet scrubbing process includeschemical processes with oxidants such as permanganese salts, dichromatesalts, ozone, perhydrogen oxide/sulfuric acid, nitric acid and the like.When an adhesive film containing a scrubbing component soluble in anoxidant or an adhesive film of a two-layer structure with a scrubbableresin composition formed on the surface is attached, the scrubbingprocess with oxidants can be efficiently carried out. After preparing ananchor with protrusions and recesses on the surface of the resincomposition, if necessary, a conductor layer is formed through dryplating such as vapor deposition, sputtering and ion plating, and/or wetplating such as non-electrolytic or electrolytic plating.

[0051] In a further embodiment, the adhesive film of the presentinvention is laminated on an internal-layer circuit board with a patternprocessed in the same manner as described above, so that the resincomposition containing the scrubbing component or the catalyzer fornonelectro-plating with metal might be on the outer side (FIGS. 3 and4). The resin composition including the catalyzer for non-electroplatingwith metal is preferred for the additive method which produces aninter-laminar adhesive film for multi-layer printed wiring boardsbecause of the use of non-electroplating. Then, a plated resist with apattern reverse to that of a conductor layer may be formed to form theconductor layer only through non-electrolytic plating. After theconductor layer is thus formed, followed by an annealing process at 130to 200° C. for 10 to 60 minutes, the curing of the thermosetting resinprogresses so that the via strength of the conductor layer can befurther improved.

[0052] A multi-layer printed wiring board produced by using theinter-laminar adhesive film of the present invention has such excellentsurface smoothness, that the process as described above can be repeatedmultiple times to laminate a build-up layer in multiple steps to preparea multi-layer printed wiring board.

EXAMPLES

[0053] The present invention will be describe specifically in thefollowing production examples, examples and comparative examples, butthe invention is not limited to these examples. The assessment method isas follows:

[0054] Flowability at ½ Depth of Through-Hole, Through-Hole Embedding,via Hole Embedding, and Embedding of Conductor Thickness in BetweenCircuit.

[0055] By observation of resin shape on cross section. The term “good”means the state where resin is filled in the hole or in between thecircuit.

[0056] Plane Smoothness on Circuit

[0057] The surface roughness on the circuit of A and B coupons definedaccording to the IPC standard was measured according to JISB 0601.

[0058] Heat Resistance of Solder

[0059] After immersion in a solder bath at 260° C. for 60 seconds, theimmersed matter was drawn up to observe visually the solder status. Theterm “good” means no abnormality in the solder status.

Example 1

[0060] Thirty parts by weight of a fluid bisphenol A epoxy resin (withan epoxy equivalent of 185, Epicoat 828 EL manufactured by Oil ShellEpoxy, Co., Ltd.) As the component A (the amount to be blended ishereinafter represented in parts by weight), 20 parts by weight of abisphenol A epoxy resin (with an epoxy equivalent of 2000 and asoftening point of 124° C., Epicion 7051 manufactured by Dai-Nippon InkChemistry, Co., Ltd.) as the component B, and 40 parts by weight of abrominated bisphenol A epoxy resin (with an epoxy equivalent of 499, asoftening point of 75° C. and a bromide content of 21% by weight,YDB-500 manufactured by Toto Chemical Industry, Co., Ltd.) weredissolved in methyl ethyl ketone (abbreviated as MEK hereinafter) underheating and agitation, to which were added epoxy curing agents as thecomponent (C), namely 4 parts by weight of2,4-diamino-6-(2-methyl-limidazolylethyl)-1,3,5-triazine isocyanuricacid adduct, 2 parts by weight of finely ground silica and 4 parts byweight of antimony trioxide to prepare a resin composition varnish. Thevarnish was coated on a polyethylene terephthalate (abbreviated as PEThereinafter) film of a thickness of 30 μm to a final dried thickness of50 μm by means of a roller coater, followed by drying at 80 to 100° C.for 10 minutes, to prepare an adhesive film (at a content of theresidual solvents at 0.5% by weight). The film was folded at an angle of180 degrees so as to assess the flexibility, and no abnormalities suchas cracks were found in the resin part.

Example 2

[0061] Twenty parts by weight of a fluid bisphenol A epoxy resin(Epicoat 828 EL manufactured by Oil Shell Epoxy, Co., Ltd.) as thecomponent A, 20 parts by weight of a brominated bisphenol A epoxy resin(YDB-500, manufactured by Toto Chemical Industry, Co., Ltd.) And 20parts by weight of cresol novolak epoxy resin (with an epoxy equivalentof 215 and a softening point of 78° C.; Epiclon N-673, manufactured byDai-Nippon Ink Chemistry, Co., Ltd) as the component B′, and 15 parts byweight of a polybutadiene rubber with its terminus epoxylated (DenalexR-45EPT, manufactured by Nagase Chemical Industry, Co., Ltd.) weredissolved in MEK under heating and agitation, to which were added 50parts by weight of a brominated phenoxy resin varnish (at a non-volatilecontent of 40% by weight and a bromide content of 25% by weight in asolvent composition of xylene: methoxypropanol: methyl ethyl keton5:2:8, YPB-40-PXM40, manufactured by Toto Chemical Industry, Co., Ltd.)as the component (D), epoxy curing agents as the component (C), namely 4parts by weight of2,4-diamino-6-(2-methyl-1-imidazolylethyl)-1,3,5-triazine isocyanuricacid adduct, and 2 parts by weight of finely ground silica and 4 partsby weight of antimony trioxide, and 5 parts by weight of calciumcarbonate as the component (E) to prepare a resin composition varnish.The varnish was coated on a PET film at a thickness of 38 μm to a finaldried thickness of 70 μm by means of a roller coater, followed by dryingat 80 to 100° C. for 12 minutes to prepare an adhesive film (at acontent of the residual solvents at 2% by weight). The film was foldedat an angle of 180 degrees so as to assess the flexibility, and noabnormalities such as cracks were found in the resin part.

Example 3

[0062] The resin composition varnish as described in Example 2 wascoated on a PET film of a thickness of 50 μm to a final dried thicknessof 100 μm by means of a roller coater, followed by drying at 80 to 120°C. for 13 minutes to prepare an adhesive film (at a content of theresidual solvents at 4% by weight). The film was folded at an angle of180 degrees so as to access the flexibility, and no abnormalities suchas cracks were found in the resin part.

Example 4

[0063] Fifty parts by weight of a brominated bisphenol A epoxy resin(YDB-500 manufactured by Toto Chemical Industry Co., Ltd.) as thecomponent (A) and 25 parts by weight of a polybutadiene rubber with itsterminus epoxylated (Denalex R-4SEPT manufactured by Nagase ChemicalIndustry, Co., Ltd.) as the component (C) were dissolved in MEK underheating and agitation to which were added epoxy during agents as thecomponent (B), namely 3 parts by weight of 2-ethyl-4-methyl imidazole, 2parts by weight of finely ground silica and 20 parts by weight ofcalcium carbonate as the component (C) to prepare a resin compositionvarnish. The varnish was coated on a PET film of a thickness of 38 μm toa final dried thickness of 5 μm by means of a roller coater, followed bydrying at 80 to 100° C. for 5 minutes for semi-curing to prepare ascrubbable resin composition (at a content of the residual solvents atless than 0. 1% by weight). Furthermore, the resin composition varnishfrom Example 1 was coated thereon to a final dried thickness of 60 μm bymeans of a roller coater, followed by drying at 80 to 100° C. for 12minutes to prepare an adhesive film of a two-layer structure comprisingresin compositions (at a content of the residual solvents of 1.5% byweight). The film was folded at an angle of 180 degrees so as to assessthe flexibility, and no abnormalities such as cracks were found in theresin part.

Example 5

[0064] Forty-five parts by weight of a thermosetting allylatedpolyphenylene ether resin and 15 parts by weight of diallyl phthalatemonomer as the component (D), 10 parts by weight of a fluid bisphenol Aepoxy resin (Epicoat 828 EL manufactured by Oil Shell Epoxy, Co., Ltd.)as the component (A), and 20 parts by weight of a cresol novolak epoxyresin (Epicon N-673, manufactured by Dai Nippon Ink Chemistry, Co.,Ltd.) as the component B′ were dissolved in MEK under heating andagitation to which were added 2 parts by weight of dicyandiamide, 0.5part by weight an organic peroxide (Perbutyl P, manufactured by NipponYushi, Co., Ltd.), 2 parts by weight of finely ground silica and 0.5part by weight a silicon leveling agent as the epoxy curing agents asthe component C to prepare a resin composition varnish. In the samemanner as in Example 4, a scrubbable resin composition of a thickness of5 μm was formed on a PET film. Still further, the resin compositionvarnish was coated thereon to a final dried thickness of 70 μm by meansof a roller coater, followed by drying at 80 to 100° C. for 12 minutesto prepare an adhesive film of a two-layer structure comprising theresin compositions (at a content of the residual solvents at 2.5% byweight). The film was folded at an angle of 180 degrees so as to assessthe flexibility, and no abnormalities such as cracks were found in theresin part.

Example 6

[0065] Ten parts by weight of a fluid bisphneol A epoxy resin (Epicoat828 EL manufactured by Oil Shell Epoxy, Co., Ltd.) and 60 parts byweight of a brominated bisphenol A epoxy resin (YDB-500, manufactured byToto Chemical Industry, Co., Ltd.) as the component (A) were dissolvedin MEK under heating and agitation to which were added 2 parts by weightof 2-ethyl-4-methyl imidazole as the epoxy curing agents as thecomponent (B), 2 parts by weight of a finely ground silica and as thecomponent (C), 2 parts by weight of Pd and PdCl₂ mixed powder(PD:PdCl₂=1:1 by weight) to prepare a resin composition varnish. Theresin composition varnish was coated on a PET film to a dried thicknessof 5 μm by means of a roller coater, followed by drying at 80 to 100°C., for 5 minutes to prepare an additive resin composition film (theamount of residual solvents was below 0.1% by weight). Furthermore, theresin composition varnish from Example 1 was coated to a final driedthickness of 60 μm by means of a roller coater, followed by drying at 80to 100° C., for 12 minutes, to prepare an adhesive film of a two-layerstructure comprising resin composition (the amount of the residualsolvents was 1.5% by weight).

[0066] The film was folded at an angle of 180 degrees so as to assessthe flexibility, and no abnormalities such as cracks were found in theresin parts.

Production Example 1

[0067] The adhesive film recovered in Example 1 was laminatedsimultaneously on both the surfaces of each of the glass epoxyinternal-layer circuit boards shown in Table 1. Preferable conditionsfor filling resins in through-holes with no void were as follows: For acontinuous process, the roll temperature was 100° C.; the pressure was 3kgf/cm²; the rate was 30 cm/minute and the vapor pressure was 2 mmHg orless. For a batch process, the roll temperature was 80° C.; the pressurewas 1 kgf/cm² and the vapor pressure was 2 mmHg or less after 5-secpressing. After standing around ambient temperature, the PET film waspeeled off, and then, a commercially available copper foil with anadhesive thereon was attached for integral curing at 170° C. for 60minutes to prepare a four-layer printed wiring board. Thereafter, agiven through-hole part and a given via hole part were pierced with adrill and/or laser, followed by non-electrolytic and/or electrolyticplating to prepare a fourlayer printed wiring board according to asubtractive process. The resulting printed wiring board was soldered at260° C. for 60 seconds, and the heat resistance against soldering wasobserved, with no abnormality.

Production Example 2

[0068] The adhesive film recovered in Example 2 was laminatedsimultaneously on both the surfaces of each of the glass epoxyinternal-layer circuit boards shown in Table 1 by means of a vacuumlaminator. Preferable conditions for filling resins in through-holeswith no void were as follows: For a continuous process, the rolltemperature was 110° C.; the pressure was 3 kgf/cm²; the rate was 30cm/minute and the vapor pressure was 30 mmHg or less. For a batchprocess, the roll temperature was 85° C.; the pressure was 1 kgf/cm² andthe vapor pressure was 2 mmHg or less after 5-sec pressing. Afterstanding around ambient temperature, the PET film was peeled offfollowed by thermal curing at 150° C. for 30 minutes, and thereafter, agiven via hole part by weight Φ0.10 was pierced with CO₂ laser. Then,the surface of the resin composition was subjected to a scrubbingprocess with an alkaline oxidant of permanganese salt, and a conductorlayer was formed over the entire surface through non-electrolytic and/orelectrolytic plating to prepare a four-layer printed wiring boardaccording to a subtractive process. Subsequently, the board wassubjected to an annealing process at 150° C. for 30 minutes to stabilizethe adhesion strength of the conductor. The via strength of theconductor was 1.0 kg/cm or more. The resulting printed wiring board wassoldered at 260° C. for 60 seconds, and the heat resistance againstsoldering was observed, with no abnormality.

Production Example 3

[0069] The adhesive film recovered in Example 3 was laminatedsimultaneously on both the surfaces of each of the glass epoxyinternal-layer circuit boards shown in Table 1 by means of a vacuumlaminator. Preferable conditions for filling resins in through-holeswith no void were as follows: For a continuous process, the rolltemperature was 110° C.; the pressure was 3 kgf/cm²; the rate was 25cm/minute; and the vapor pressure was 30 mmHg or less. For a batchprocess, the roll temperature was 90° C.; the pressure was 1 kgf/cm² andthe vapor pressure was 2 mmHg or less after 6-sec pressing. Afterstanding around ambient temperature, the PET film was peeled offfollowed by thermal curing at 150° C. for 30 minutes, and thereafter, agiven via hole part by weight Φ0.10 was pierced with CO₂ laser. Then,the surface of the resin composition was subjected to a scrubbingprocess with an alkaline oxidant of permanganese salt to form a platedresist of a reverse pattern to that of the conductor layer to prepare afour-layer printed wiring board according to an additive process.Subsequently, the board was subjected to an annealing process at 150° C.for 60 minutes to stabilize the adhesion strength of the conductor. Thevia strength of the conductor was 1.0 kg/cm or more. The resultingprinted wiring board was soldered at 260° C. for 60 seconds, and theheat resistance against soldering was observed, with no abnormality.

Production Example 4

[0070] The adhesive film recovered in Example 4 was laminatedsimultaneously on both the surfaces of each of the glass epoxyinternal-layer circuit boards shown in Table 1 by means of a vacuumlaminator. Preferable conditions for filling resins in through-holeswith no void were as follows: For a continuous process, the rolltemperature was 100° C.; the pressure was 3 kgf/cm²; the rate was 30cm/minute; and the vapor pressure was 30 mmhg or less. For a batchprocess, the roll temperature was 80° C.; the pressure was 1 kgf/cm² andthe vapor pressure was 2 mmHg or less after 5-sec pressing. Afterstanding around ambient temperature, the PET film was peeled offfollowed by thermal curing at 170° C. for 30 minutes, and thereafter, agiven via hole part and a given through-hole part were pierced with adrill and/or laser. Then, the surface of the resin composition wassubjected to a scrubbing process with an alkaline oxidant ofpermanganese salt, and a conductor layer was formed on the entiresurface through non-electrolytic and/or electrolytic plating to preparea four-layer printed wiring board according to a subtractive process.The via strength of the conductor was 1.0 kg/cm or more. The resultingprinted wiring board was soldered at 260° C. for 60 seconds, and theheat resistance against soldering was observed, with no abnormality.

Production Example 5

[0071] The adhesive film recovered in Example 5 was laminatedsimultaneously on both the surfaces of each of the glass epoxyinternal-layer circuit boards shown in Table 1 by means of a vacuumlaminator. Preferable conditions for filling resins in through-holeswith no void were as follows: For a continuous process, the rolltemperature was 120° C.; the pressure was kgf/cm²; the rate was 35cm/minute; and the vapor pressure was 30 mmHg or less. For a batchprocess, the roll temperature was 95° C.; the pressure was 1 kgf/cm² andthe vapor pressure was 2 mmHg or less after 6-sec pressing. Afterstanding around ambient temperature, the PET film was peeled offfollowed by thermal curing at 180° C. for 60 minutes, and thereafter, agiven via hole part and a given through-hole part were pierced with adrill and/or laser. Then, the surface of the resin composition wassubjected to a scrubbing process with an alkaline oxidant ofpermanganese salt to form a plated resist of a reverse pattern to thatof the conductor layer to prepare a four-layer printed wiring boardaccording to an additive process. The via strength of the conductor was1.0 kg/cm or more. The resulting printed wiring board was soldered at260° C. for 60 seconds, and the heat resistance against soldering wasobserved, with no abnormality.

Production Example 6

[0072] By means of a vacuum laminator, the adhesive film recovered inExample 2 was laminated simultaneously on both the faces of aninternal-layer circuit board comprising the four-layer printed wiringboard produced in the Production Example 2, having a board thickness of0.09 mm and a conductor thickness of 25 μm and with a superficial viahole of Φ0.10. Preferable conditions for filling resins in thesuperficial via hole with no void were as follows: For a continuousprocess, the roll temperature was 110° C.; the pressure was 1.5 kgf/cm²;the rate was 25 cm/minute; and the vapor pressure was 30 mmHg or less.For a batch process, the roll temperature was 85° C.; the pressure was 1kgf/cm² and the vapor pressure was 2 mmHg or less after 5-sec pressing.After standing around ambient temperature, the PET film was peeled offfollowed by thermal curing at 150° C. for 30 minutes. Thereafter, agiven via hole part of Φ0.10 and the like were pierced with CO₂ laser.Then, the surface of the resin composition was subjected to a scrubbingprocess with an alkaline oxidant of permanganese salt, and then,non-electrolytic and/or electrolytic copper plating was done on thewhole surface thereof, to prepare a conductor layer. Subsequently, apattern was formed according to a subtractive process, followed by anannealing process at 50° C. for 30 minutes to prepare a six-layerprinted wiring board. The via strength of the conductor was 1.0 kg/cm ormore. The resulting printed wiring board was soldered at 260° C. for 60seconds, and the heat resistance against soldering was observed, with noabnormality.

Production Example 7

[0073] The adhesive film recovered in Example 2 was laminatedsimultaneously on both the faces of each of the internal-layer circuitboards shown in Table 1 by means of a vacuum laminator, in the samemanner as in the Production Example 2. The PET film was peeled offfollowed by thermal curing at 150° C. for 30 minutes. Thereafter, agiven via hole part by weight Φ0.10 was pierced with CO₂ laser. Then, acopper foil of a thickness of 0.2 μm was formed on the resin compositionby a sputtering process, followed by the formation of a conductor layeron the whole surface by electrolytic copper plating to prepare afour-layer printed wiring board by a subtractive process, followed by anannealing process at 150° C. for minutes to stabilize the adhesionstrength of the conductor. The via strength of the conductor was 1.0kg/cm or more. The resulting printed wiring board was soldered at 260°C. for 60 seconds, and the heat resistance against soldering wasobserved, with no abnormality.

Production Example 8

[0074] The adhesive film recovered in Example 6 was laminatedsimultaneously on both the surfaces of each of the glass epoxyinternal-layer circuit boards shown in Table 1 by means of a vacuumlaminator. Preferable conditions for filling resins in through-holeswith no void were as follows: For a continuous process, the rolltemperature was 100° C.; the pressure was 3 kgf/cm²; the rate was 30cm/minute; and the vapor pressure was 30 mmHg or less. For a batchprocess, the roll temperature was 80° C.; the pressure was 1 kgf/cm² andthe vapor pressure was 2 mmHg or less after 5-sec pressing. Afterstanding around ambient temperature, the PET film was peeled offfollowed by thermal curing at 170° C. for 30 minutes, and thereafter, agiven via hole part and a given through-hole part were pierced with adrill and/or laser. Then, the surface of the resin composition wassubjected to a desmearing process with an alkaline oxidant ofpermanganese salt, and a conductor layer was formed on the entiresurface through non-electrolytic and/or electrolytic plating to preparea four-layer printed wiring board according to an additive process. Thevia strength of the conductor was 1.0 kg/cm or more. The resultingprinted wiring board was soldered at 260° C. for 60 seconds, and theheat resistance against soldering was observed, with no abnormality.

Comparative Examples 1 and 2

[0075] In the same manner as in Example, 1, an adhesive film wasprepared (at a residual solvent content of 0.5% by weight) except thatthe amount of the fluid bisphenol A epoxy resin as the component (A) tobe added was reduced to 5 parts (Comparative Example 1) or was elevatedto 120 parts (Comparative Example 2). For assessing the flexibility, theresulting film of Comparative Example 1 (at a fluid content of 7% byweight) was folded at an angle of 180 degrees. Cracking occurred in theadhesive layer, and due to such insufficient flexibility, the film wasvery difficult to handle. The film of Comparative Example 2 (at acontent of the fluid component being 63% by weight) was highly fluid atambient temperature, involving oozing because of edge fusion, so thatthe film could not be handled as film.

Comparative Example 3

[0076] In the same manner as in Example 1, an adhesive film was prepared(at a residual solvent content of 0.5% by weight) except that the wholeamount of the bisphenol A epoxy resin (Epicion 7051 manufactured byDai-Nippon Ink Chemistry, Co., Ltd.) as the component (B) was replacedwith 60 parts by weight of a brominated bisphenol A epoxy resin (YDB-500manufactured by Toto Chemical Industry, Co., Ltd.). For assessing theflexibility, the resulting film was folded at an angel of 180 degrees.No abnormalities such as cracking occurred in the resin part.

Comparative Example 4

[0077] In the same manner as in Example 2, an adhesive film was prepared(at a residual solvent content of 2% by weight; 42% by weight of thescrubbing component and 36% by weight of the inorganic component as the(E)), except that the amount of calcium carbonate as the component (E)was elevated to 50 parts by weight. For assessing the flexibility, theresulting film was folded at an angle of 180 degrees. No abnormalityincluding cracking occurred in the resin part.

Comparative Production Example 1

[0078] The adhesive film prepared in Comparative Example 1 was laminatedsimultaneously on both the faces of the same glass epoxy internal-layercircuit board as in the Production Example 1 by means of a vacuumlaminator. Under the same lamination conditions as in the ProductionExample 1, namely at a roller temperature of 100° C. and a rate of 30cm/minute for a continuous process and a temperature of 80° C. for batchprocess, the laminate temperature of the resin composition of theadhesive film was less than 75° C. At the maximum roll pressure of 8kgf/cm² for a continuous process and at the maximum roller pressure of 6kgf/cm² for a batch process, voids remained in the through-hole, whichcould not be filled with the resin.

Comparative Production Example 2

[0079] The adhesive film prepared in Comparative Example 3 was laminatedsimultaneously on both the faces of the same glass epoxy internal-layercircuit board as in the Production Example 1 by means of a vacuumlaminator. Under the same lamination conditions as in the ProductionExample 1, resin oozing occurred strongly, so that the film could not belaminated at a uniform resin thickness on the internal-layer circuit.Additionally, resin cissing occurred on the conductor during curingunder heating, so that a more non-uniform thickness is caused.

Comparative Production Example 3

[0080] The adhesive film prepared in Comparative Example 4 was laminatedsimultaneously on both the faces of the same glass epoxy internal-layercircuit board as in the Production Example 2 by means of a vacuumlaminator. Preferable conditions for filling resins in through-holeswith no void were as follows: For a continuous process, the rolltemperature was 115° C.; the pressure was 3 kgf/cm²; the rate was 25cm/minute and the vapor pressure was 30 mmHg or less. For a batchprocess, the roll temperature was 90° C.; the pressure was 1 kgf/cm² andthe vapor pressure was 2 mmHg or less after 5-sec pressing. Afterstanding around ambient temperature, the PET film was peeled off, forsubsequent curing at 150° C. for minutes. Thereafter, a giventhrough-hole part of Φ0.10 was pierced with CO₂ laser. The opening ofthe via was at about 0.01 mm, but the bottom was less than the half, andthe via side wall was fragile, which means no reliability in the platingprocess. Additionally, piercing of a via hole of Φ0.10 was attempted bymeans of UV laser, but compared with the film of Example 2, theresulting via side wall was dirty and the processing time was long.Then, the surface of the adhesive was subjected to a scrubbing processwith an alkaline oxidant of permanganese salt to form a conductor layeron the whole surface by non-electrolytic and/or electrolytic plating,and then prepare a four-layer printed wiring board according to asubtractive process. The resulting via strength of the conductor was 1.0kg/cm or more. The printed wiring board was soldered at 260° C. for 60seconds, and the heat resistance against soldering was observed.Abnormalities including expansion and conductor peeling were observed.

[0081] The results of Examples 1 to 6 and Production Examples 1 to 8indicate that the coating of an internal-layer circuit pattern and/orthe resin filling in superficial via holes can be integrally andsimultaneously carried out in accordance with the present invention andthat a multi-layer printed wiring board can be prepared at a highproductivity by using the same. The results of Comparative Examples 1and 2 indicate that to handle the epoxy resin composition of the presentinvention as film, the fluid component should importantly be within arange of 10 to 55% by weight in the resin composition. The results ofComparative Production Example 1 additionally indicate that at a contentof a resin with a softening point lower than the laminate temperaturebeing less than 10% by weight in the resin composition, even a higherlaminate pressure can hardly embed resin with no void in thethrough-hole; if no component suppressing thermal fluidity duringlamination was contained as in Comparative Production Example 2, goodlamination could not be effected. If scrubbing component with poor heatresistance and poor chemical resistance was contained at 40% by weightor more as in Comparative Production Example 3, the resulting film couldnot be used practically as an inter-laminar insulation material, thoughthe via strength of the resulting plated conductor could be procured. Ifthe inorganic component was above 30% by weight, furthermore, the via ofa small diameter of 100 μm or less was fallen into a poor shape, evenafter a process of CO₂ laser and UV laser, causing problems in terms ofconnection reliability; additionally, such a resin composition had poorlaser piercing property, for example, the resin composition caused thereduction of laser processing rate. If even a scrubbable resincomposition containing a scrubbing component at 40% by weight or morewas prepared as an adhesive film of a two-layer structure as in Example4 or 5, the via strength and reliability could be establishedconcurrently in a simple manner.

[0082] By the method of the present invention, an inter-laminar adhesivefilm for multi-layer printed wiring boards can be prepared, havingexcellent embedding property of the internallayer circuit and excellentsurface smoothness, and by using the adhesive film, a multi-layerprinted wiring board can be produced at a build-up process at a highproductivity.

[0083] Obviously, additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

We claim:
 1. A process for producing a multi-layer printed wiring boardcomprising the steps of: providing an inter-laminar adhesive film,wherein said inter-laminar adhesive film comprises a support film baselayer and a resin composition that is solid at ambient temperatures;providing an internal-layer circuit board having an electric conductorlayer pattern thereon; laminating said inter-laminar adhesive film tosaid internal-layer circuit board electric conductor layer pattern underlamination conditions; wherein, under said lamination conditions, saidresin composition has a resin flow that is of the depth of a superficialvia hole, if present, in the internal layer circuit; or the resin flowis ½-fold or more the depth of a through-hole, if present, in theinternal-layer circuit board.
 2. A process for producing a multi-layerprinted wiring board comprising the steps of: providing an inter-laminaradhesive film for laminating, wherein said adhesive film comprises asupport film base layer and a resin composition that is solid at ambienttemperatures; providing an internal-layer circuit board having anelectrical conductor pattern thereon; laminating said inter-laminaradhesive film to the surface of the internal-layer circuit board bycontacting the surface of the internal-layer circuit board with theresin composition layer under lamination conditions, including alamination temperature and pressure, thereby adhering the inter-laminaradhesive film to the surface of the internal-layer circuit board;wherein at least 10% by weight of the resin composition layer comprisesa resin having a softening point lower than the lamination temperature,and the resin composition has a thickness greater than a thickness ofthe electric conductor layer; and wherein, under the laminationconditions, the resin composition has a resin flow that: (i) is at leastof the thickness of the electric conductor, (ii) is at least the depthof a superficial via hole, if present, in the internal-layer circuitboard, or (iii) is ½-fold or more the depth of a through-hole, ifpresent, in the internal-layer circuit board singly or in combinationwith a superficial via hole.
 3. A process for producing a multi-layerprinted wiring board comprising the steps of: providing aninternal-layer circuit board having an electrical conductor patternthereon; providing an inter-laminar adhesive film, which comprises asupport film base layer and a layer of a resin composition that is solidat ambient temperature; laminating said inter-laminar adhesive film tothe internal-layer circuit board by contacting the surface of theinternal-layer circuit board with the resin composition layer underlamination conditions, including a lamination temperature and pressure,thereby adhering the inter-laminar adhesive film to the surface of theinternal-layer circuit board; wherein said resin composition comprises:(A) an epoxy resin that is liquid at ambient temperature; (B) apolyfunctional epoxy resin with a softening point higher than thelamination temperature and having two or more epoxy groups per epoxyresin molecule; and (C) a latent epoxy curing agent capable ofinitiating a reaction at a temperature higher than the laminationtemperature.
 4. The process of claim 3, wherein said resin compositionfurther comprises from 10 to 55% by weight of the composition of aliquid resin other than the liquid epoxy resin (A) or an organic solventor a combination thereof.
 5. A process for producing a multi-layerprinted wiring board comprising the steps of: providing aninternal-layer circuit board having an electric conductor patternthereon; providing an inter-laminar adhesive film, which comprises asupport film base layer and a resin composition that is solid at ambienttemperature; laminating said inter-laminar adhesive film to theinternal-layer circuit board by contacting the surface of theinternal-layer circuit board with the resin composition layer underlaminating conditions, including a lamination temperature and pressure,thereby adhering the inter-laminar adhesive film to the surface of theinternal-layer circuit board; wherein said resin composition comprises:(A) an epoxy resin that is liquid at ambient temperature; (B) apolyfunctional epoxy resin with a softening point lower than thelamination temperature and having two or more epoxy groups per epoxyresin molecule; (C) a latent epoxy curing agent capable of initiating areaction at a temperature higher than the lamination temperature; and(D) a binder polymer with a weight average molecular weight within arange of 5,000 to 100,000.
 6. The process of claim 5, wherein said resincomposition further comprises from 10 to 55% of a liquid resin otherthan the liquid epoxy resin (A) or an organic solvent or a combinationthereof; and wherein component (D) constitutes from 5 to 50% by weightof the composition.
 7. The process according to claim 1, 2, 3, 4 or 5,wherein the resin composition further comprises (i) at least onescrubbing component selected from the group consisting of rubbercomponents, amino resins, inorganic fillers, organic fillers, or (ii) atleast one electroless plating catalyst selected from the groupconsisting of metals, metal compounds and inorganic compositions havingmetal or metal compounds absorbed or coated thereon, or a combinationthereof, wherein the scrubbing component constitutes 5 to 40% by weightof the resin composition, and wherein the said electroless platingcatalyst constitutes 0.05 to 3% by weight of the resin composition. 8.The process according to claim 1, 2, 3, 4, or 5, wherein saidinter-laminar adhesive film comprises a layer of a scrubbable resincomposition solid at ambient temperature interposed between said supportfilm base layer and said solid resin composition, wherein saidscrubbable resin composition comprises: (a) a polyfunctional epoxy resinhaving two or more epoxy groups per epoxy resin molecule; (b) an epoxycuring agent; and (c) at least one scrubbing component selected from thegroup consisting of rubber components, amino resins, inorganic fillers,and organic fillers.
 9. The process of claim 8, wherein said scrubbableresin composition further comprises an organic solvent.
 10. The processaccording to claim 8, wherein said scrubbable resin composition furthercomprises at least one electroless plating catalyst selected from thegroup consisting of metals, metal compounds, and inorganic compositionshaving metal or metal compounds absorbed or coated thereon.
 11. Theprocess according to claim 1, 2, 3, 4 or 5 wherein said inter-laminaradhesive film comprises a layer of an additive resin composition solidat ambient temperature interposed between said support film base layerand said solid resin composition, wherein the additive resin compositioncomprises: (a) a polyfunctional epoxy resin having two or more epoxygroups per epoxy resin molecule; (b) an epoxy curing agent; and (c) atleast one electroless plating catalyst selected from the groupconsisting of metals, metal compounds, and inorganic compositions havingmetal or metal compounds absorbed or coated thereon.
 12. The processaccording to claim 1, 2, 3, 4, or 5 wherein said process furthercomprises: (i) peeling off the support base film layer and optionallythermally curing the resin composition subsequent to laminating theinter-laminar adhesive film, and (ii) laminating a copper foil on theoptionally thermally cured adhesive layer by the use of heat oradhesive.
 13. The process according to claim 1, 2, 3, 4, or 5 whereinsaid lamination conditions are selected from temperatures for contactbonding in the range of from 70 to 200° C., pressure in the range offrom 1 to 10 kgf/cm² and reduced pressures of 1 to 20 mmHg.
 14. Theprocess according to claim 13, wherein said process further comprises:(i) peeling off the support base film and optionally, thermally curingthe resin composition subsequent to laminating the inter-laminaradhesive film; and (ii) laminating a copper foil on the optionallythermally cured adhesive layer by the use of heat or adhesive.
 15. Theprocess according to claim 1, 2, 3, 4 or 5 wherein said process furthercomprises: (i) peeling off the support base film and optionallythermally curing the resin composition subsequent to laminating theinter-laminar adhesive film; (ii) piercing the optionally cured resincomposition by means of laser or drill; (iii) scrubbing the surface ofthe optionally cured resin composition by a dry process and optionally,a wet process; and (iv) forming a conductor layer as an upper layerthereof by dry plating and optionally wet plating.
 16. The processaccording to claim 15, wherein said process further comprises: (i)peeling off the support base film and optionally, thermally curing theresin composition subsequent to laminating the inter-laminar adhesivefilm; (ii) piercing the optionally cured resin composition by means oflaser or drill; (iii) scrubbing the surface of the optionally curedresin composition by a dry process and optionally a wet process; and(iv) forming a conductor layer as an upper layer thereof by dry platingand optionally wet plating.
 17. A multi-layer printed wiring boardproduced by the process of claim
 1. 18. A multi-layer printed wiringboard produced by the process of claim
 2. 19. A multi-layer printedwiring board produced by the process of claim
 3. 20. A multi-layerprinted wiring board produced by the process of claim
 4. 21. Amulti-layer printed wiring board produced by the process of claim
 5. 22.A multi-layer printed wiring board produced by the process of claim 8.23. A multi-layer printed wiring board produced by the process of claim11.
 24. A multi-layer printed wiring board produced by the process ofclaim
 12. 25. A multi-layer printed wiring board produced by the processof claim
 13. 26. A multi-layer printed wiring board produced by theprocess of claim
 15. 27. A multi-layer printed wiring board produced bythe process of claim 16.